http://jsfiddle.net/1744v90y/1/NOTE:It seems that with Font Awesome version 5 this approach currently doesn't work.The example is using Font Awesome version 4.7.

But we currently don't support HTML in items. That means stacked icons are not currently possible in that way.

One way that you can try, is create your own HTML and bind it to the nodes based on the nodes coordinates.Here is an example with popup, but similar approach can be used in your case for multiple nodes.

I updated my solution to fontawesome 5. I am working with Unicode of icons so now I have to set font-width property. I tried several ways but nothing worked. Like:textStyle: { fillColor: "black", font: "Font Awesome 5 Free", "font-weight": "900" },As I currently expected there is no font-weight property for textStyle.You wrote